This post summarizes how I install and dual-boot Arch GNU/Linux with
Full-Disk Encryption alongside macOS. It is not meant to be a
replacement for the Installation Guide or the former Beginner’s Guide.
Rather, it mostly serves as a small summary with a few useful notes
about the gotchas.

So, make sure you understand what you type into your terminal. If you
don’t, checking out the Arch wiki should probably be your first step.

Note: you will need internet access throughout the installation and
the MacBook Air’s WiFi doesn’t work out of the box on Arch. I
recommend using your phone’s USB Tethering (if it does support it), or
using an Ethernet-USB adapter.

The first step I take is resizing the HFS+ macOS partition to make
room for the new GNU/Linux installation. There are plenty
of tutorials on how to do this using macOS’s Disk Utility, so do that
and then come back!

There are different ways of creating a bootable Arch USB, all
documented on the USB flash installation media page on the Arch wiki,
but the simplest one is using dd if you already have access to
another UNIX system.

Warning: make sure you backup the data on your flash
drive, as dd will irrevocably destroy all data on it.

Use lsblk to find the name (block device) of your USB drive, then
run dd (as root) as shown below:

This will create a physical volume on the mapping we just opened,
create a volume group named vg on the physical volume, and create a
logical volume named root that spans the entire volume group. More
complex setups are possible thanks to the great flexibility of lvm.

Then adjust the initramfs hooks in /etc/mkinitcpio.conf and enable
the encrypt and lvm2 hooks, and make sure keyboard is available
before encrypt so you can actually type in the LUKS password when
booting. Your HOOKS line should look similar to this:

At this point, I usually install my favorite AUR helper, pacaur, then
I install the broadcom-wl-dkms wireless driver and mba6x_bl-dkms
backlight driver to fix the post suspend/resume issue where three’s no
brightness after waking up from suspend, and the only available
brightness would be 100%.